Honor DNS server from DHCP

PUBLISHED_FROM=10772301ef115c31ada3521ff4235c33a421b782

docs/c-api/net.h/struct_mg_connect_opts.md

@@ -8,6 +8,7 @@ signature: |
     unsigned int flags;        /* Extra connection flags */
     const char **error_string; /* Placeholder for the error string */
     struct mg_iface *iface;    /* Interface instance */
+    const char *nameserver;    /* DNS server to use, NULL for default */
   #if MG_ENABLE_SSL
     /*
      * SSL settings.

docs/c-api/net.h/struct_mg_mgr.md

@@ -17,6 +17,7 @@ signature: |
   #if MG_ENABLE_JAVASCRIPT
     struct v7 *v7;
   #endif
+    const char *nameserver; /* DNS server to use */
   };
 ---
 

docs/c-api/net.h/struct_mg_mgr_init_opts.md

@@ -7,6 +7,7 @@ signature: |
     const struct mg_iface_vtable *main_iface;
     int num_ifaces;
     const struct mg_iface_vtable **ifaces;
+    const char *nameserver;
   };
 ---